The present invention claims the benefit of Korean Patent Application No. 2002-84895 filed in Korea on Dec. 27, 2003, which is hereby incorporated by reference
1. Field of the Invention
The present invention relates to a liquid crystal display module, more particularly to a liquid crystal display module having a direct-below-type back light and assembling method thereof.
2. Description of the Related Art
In general, the trend in liquid crystal display (hereinafter, LCD) has been a gradually widening application scope due to the lightness, thin profile and low power consumption of a liquid crystal panel. In accordance with this trend, the LCD is now used in office automation devices, audio/video device, etc. The LCD transmits a quantity of light through a matrix of pixels in accordance with an image signal applied to control switches within the pixels to display desired pictures in a screen.
The LCD is not a spontaneous light-emitting display and needs a back light as a light source. The two types of back light for LCD are direct-below-type and an edge-type. The edge-type LCD has a fluorescent lamp installed on the outside of a transparent optical guide plate. Thus, light is made incident upon the entire surface of a liquid crystal panel by using the transparent optical guide plate from the fluorescent lamp. The direct-below-type LCD has the light source arranged directly below a rear surface of the liquid crystal panel and directly radiates light onto the entire rear surface of the liquid crystal panel. As compared with the edge-type LCD, the direct-below-type LCD has the advantage of using a plurality of light sources, which can improve brightness and provide light for larger liquid crystal panels.
FIG. 1 is a cross-sectional view illustrating a liquid crystal display module adopting a related art direct-below-type back light unit. As shown in FIG. 1, the liquid crystal panel module 1 includes a direct-below-type back light unit 30, a liquid crystal panel 4 stacked on the direct-below-type back light unit 30. A guide panel 6 for supporting the liquid crystal panel 4 is placed between the direct-below-type back light unit 30 and the liquid crystal panel 4. A top case 8 encloses the border of the liquid crystal panel 4 and the side surface of the guide panel 6.
The liquid crystal panel 4 includes a thin film transistor array substrate 4a, a color filter array substrate 4b, and liquid crystal materials (not shown) injected between the thin film transistor array substrate 4a and the color filter array substrate 4b. Red (R), green (G), and blue (B) colored filters and a black matrix are located on the color filter array substrate 4b. Liquid crystal cells are arranged in an active matrix on the thin film transistor array substrate 4a. Each of cells respectively has a thin film transistor for switching a video signal to the cell. Video signals applied to the cells change the index of refraction in the liquid crystal cells to thereby display pictures corresponding to the video signals.
A tape carrier package (not shown) having a driver integrated circuit mounted thereon is installed on the thin film transistor array substrate 4a of the liquid crystal panel 4, wherein the driver integrated circuit is used to supply driving signals to the thin film transistors. The guide panel 6 is a mold, and has a supporting member in which the liquid crystal panel 4 is installed and supported. The top case 8 has a plane face and a side face bent vertically which are fabricated in a square band shape. The top case 8 is formed to enclose the edge of the liquid crystal panel 4 and the guide panel 6.
FIG. 2 is a perspective view of a portion of the direct-below-type back light unit shown in FIG. 1. A cross-sectional view illustrating the direct-below-type back light unit shown in FIG. 1 along the line I-I′ is shown in FIG. 3. Referring to FIG. 2 and FIG. 3, the direct-below-type back light unit 30 includes a bottom cover 2 and a reflection plate 14 attached to the front of the bottom cover 2. A plurality of lamps 12 are located above the bottom cover 2. A diffusion plate 16 covers the entire front surface of the bottom cover 2. Optical sheets (not shown) are located on the diffusion plate 16. Support sides 18 cover the ends of lamps 12 and are installed on both sides of the bottom cover 2. The support sides 18 have openings 19 that receive the lamps 12.
The bottom cover 2 has a bottom surface 2b and an inclined surface 2a extended from the bottom surface 2b. The bottom surface 2b together with the inclined surface 2a form a step. Projections 22 are formed in a designated interval along both sides of the bottom surface 2b of the bottom cover 2.
The support side 18 has an inclined surface with a specified slope and openings 19 in which lamps 12 are inserted. The support sides 18 are used to support the lamps 12 inserted in the openings 19. These support sides 18 are attached to the bottom cover 2 using screws (not shown). The rear surfaces of the support sides 18, shown in FIG. 1, have many holes into which the projections 22 on the bottom cover 2 are inserted.
FIG. 4 is a perspective view illustrating a jig. As illustrated in FIG. 4, to insert each of the lamps 12 into the openings 19 of the support sides 18, a jig 28 corresponding to the length of the lamps 12 is used. The support sides 18 serve as a lamp holder supporting many lamps 12. The surface of the support sides 18 are coated with reflective materials, such as aluminim (Al). The support sides 18 reflect light to the liquid crystal panel 4 so as to improve the efficiency of light incidence upon the liquid crystal panel 4.
The reflection plate 14 is made of aluminum (Al) material and is the same shape as the bottom cover 2. Further, the reflection plate 14 has a bottom surface overlapping the bottom surface 2a of the bottom cover 2 and an inclined surface correspondingly bent to the inclined surface 2b of the bottom cover 2. The reflection plate 14 is attached to the bottom surface 2b and the inclination surface 2a of the bottom cover 2 using double-sided adhesive tapes 24. That is, the bottom surface 2b of the bottom cover 2 is adhered to one side of the double-sided adhesive tape 24, and the rear surface of the reflection plate 14 is adhered to the other side of the double-sided adhesive tape 24. Hence, the reflection plate 14 is attached to the front surface of the bottom cover 2 by using the double-sided adhesive tape 24. This reflection plate 14 reflects lights from lamps 12 to the liquid crystal panel 4 to thereby improve the efficiency of light incidence upon the liquid crystal panel 4.
Each of the lamps 12 comprises a glass tube filled with inert gases that has a cathode and an anode respectively installed at the opposite ends of the glass tube. Phosphorus is on the inside wall of the glass tube. The plurality of the lamps 12 are grouped into collections with size n (where n is a positive integer) and a collection of lamps are inserted into a lamp holder 10.
The diffusion plate 16 enables the light radiated from the lamps 12 to go toward the liquid crystal panel 4 with wide range of incident angles and spreads the light out. The diffusion plate 16 includes a transparent resin film. Both surfaces of the resin film are coated with light-diffusion materials.
The light radiated from the diffusion plate 16 is diffused light. The efficiency of light through the liquid crystal display is higher when the incident light is perpendicular to the liquid crystal panel 4. For this reason, many optical sheets (not shown) are placed on the diffusion plate 16. The optical sheets (not shown) make the light from the diffusion plate 16 become perpendicular the liquid crystal panel 4, and hence improve the brightness of the liquid crystal display module 1 and hence reduce power consumption. Thus, the light from the diffusion plate 16 reaches the liquid crystal panel 4 via a plurality of optical sheets.
In order to insert the lamps 12 into the support sides 18, the support sides 18 are fixed using a jig 28 corresponding to the length of each of the lamps 12, and then the lamps 12 are inserted into the openings 19 in the support sides 18. After inserting the lamps 12 with the support sides 18, the support sides 18 and the bottom cover 2 are coupled using screws (not shown).
FIGS. 5a to 5e illustrate the successive steps of a method to assemble a related art direct-below-type back light unit of a liquid crystal display module. An assembling method for the liquid crystal display module adopting the related art direct-below-type back light unit is fully explained with reference to FIGS. 5a to 5e. The bottom cover 2, shown in FIG. 5a, is open except for the inclined surface 2a and the bottom surface 2b. The refection plate 14 made of aluminum (Al) is stacked on the bottom cover 2, and then the bottom cover 2 and the reflection plate 14 are glued together using the double-sided tape 24.
As shown in FIG. 5b, a jig 28 is used to fix the support sides 18 so that the lamps 12 can be inserted into the fixed support sides 18. Then, the jig 28 is removed from the support sides 18, and as shown in FIG. 5c, the support sides 18 with the lamps 12 inserted are combined with the bottom cover 2. The bottom cover 2 and the support sides 18 combined with the lamps 12 are coupled using screws (not shown). Thereafter, the guide panel 6 shown in FIG. 5d is coupled to the bottom cover 2, which has the support sides 18 and lamps 12. Thus, the direct-below-type back light unit 30, as shown in FIG. 5e, is assembled.
As mentioned above, the direct-below-type back light unit 30 of the liquid crystal display module 1 uses a reflective coating on the support sides 18 for reflecting light to the liquid crystal panel 4. This reflective coating is typically made of aluminum (Al), which is expensive. Also, since a jig 28 has to be used to fix the support sides 18 during step of inserting the lamps 12 into the support sides 18, assembly time is increased.